A way to carry out down-the-hole drilling in ordinary metal pipe drilling in a deviant manner from traditional asymmetric wing drilling technique is known e.g. from Finnish Patent No. 95618. A drilling head in a drilling unit of the drilling apparatus presented in this patent, existing inside a casing part or in other words a so called earth pipe or casing pipe, is formed of a first frame part and an annular second frame part, the drilling surfaces of which being provided with drilling organs, such as drill bits or like, of the first and second drilling means or in other words of a center drill or a pilot and a reaming drill or a reamer. In this solution the first frame part comprising the first drilling means, is being released from the second frame part comprising the reamer, in order to pull the same alone off from a drilled hole after the drilling situation.
In the solution in question, the second organs of the flushing means for removal of drilling waste being generated are arranged to lead drilling waste by means of an assembly, which locks the said drilling means together for a drilling situation unrotatively in respect with each other and in both directions longitudinally, which is in other words carried out as an advantageous embodiment by loosening grooves of a bayonet coupling, being placed longitudinally on a side surface of the first frame part.
In connection with a drilling device of the type described above, typically a casing shoe is being used at the end of the casing part, by means of which the casing part is pulled into the hole to be drilled by a power influence (F) that is directed to the casing shoe either from the pilot or the reamer. E.g. in FIG. 3 presenting prior art, the power influence pulling the casing part into the hole is transmitted by counterparts in the casing shoe (8) and the pilot. In the implementation in question, there has been exploited furthermore screw joint principle in the binding means (L) connecting the casing shoe and the reamer in a way that the parts in question can be coupled with each other in a lockable manner in the longitudinal direction by a screw joint, whereby the parts in question stay axially together though the mutual bayonet locking between the pilot and the reamer is opened. Respectively in FIGS. 1 and 2 presenting prior art there has been presented for their part structures, in which the casing part is being pulled through binding means between the casing shoe and the reamer that is by one or in the longitudinal direction two pulling shoulder assemblies one after the other in the parts in question.
Furthermore e.g. from patent EP 1144797 it is known to exploit a so called shrinking method in forming of the binding means between a casing shoe and a rotationally symmetrical drill, in which case the casing shoe is being pressed radially in a way that a locking projection therein gets coupled with a corresponding locking recess in the drill. This kind of a mounting requires high power in order to carry out the press binding, which is why the method in question is applicable usually for coupling of structures, having a maximum outer diameter of 300 mm.
Putting together of a drilling head according to FIG. 1 takes place typically so that an essentially elongated, in a manner of speaking sleeve-like, casing shoe is being cut during a mounting phase in a machine shop longitudinally at one point and spread open, whereafter it is being pressed together over the reamer. After this, it is being welded by its cutting point back to form once again as a uniform ring. The most remarkable disadvantage of this kind of a structure, being welded together, is the weak point due to the welding seam in the casing shoe, which gets very easily broken under difficult circumstances. A further disadvantage of this solution are thus those “extra” working phases related thereto, because the casing shoe must first of all be cut longitudinally, pressed onto the reamer and finally once again welded together. The drilling device according to FIG. 2 is being put together by the shrinking method explained above that is by pressing and the one shown in FIG. 3 by using a screw joint, in which case the screw joint does not, however, carry load during drilling.
Furthermore particularly applications for use of so called plastic pipe drilling typically e.g. well drilling or e.g. forepoling come into question. An advantage of use of a plastic pipe in drilling is first of all the fact that plastic pipes are very light compared to steel pipes, thanks to which they also have more profitable transport costs and they are easier to handle at a construction site. Furthermore a plastic pipe is significantly cheaper than a corresponding steel pipe. A plastic pipe does not rust for that matter and when being mounted into the ground, it does not break the bits of crushers or drills, when the soil is later on being e.g. worked or drilled. Furthermore in caves or quarries, metal may not blend with broken rocks, which is why use of plastic pipes in drilling has a very remarkable meaning in that context as well.
Today significant problems are, however, related to plastic pipe drilling, which is why it is not possible to exploit the same to the extent that there is a need for or that there are possibilities in practice. This is among other things due to the fact that the present arrangements require first of all use of a steel pipe in the beginning of drilling, whereby it is only after that possible to start using in the drilling a plastic pipe to be coupled with the steel pipe e.g. by a screw joint and after that further plastic pipes to be coupled with each other one after the other. On the other hand solutions are being used, which are based on a screw joint coupling between a plastic pipe with a readymade threading and a casing shoe.
The former solution is not satisfactory first of all due to the fact that there is still a need for use of a steel pipe in the starting phase, whereby it is possible to exploit plastic pipes with preworked threadings only after the above phase. On the other hand use of plastic pipes with readymade threadings has, however, found out to be also very difficult in practice, because a threaded part of a plastic pipe being coupled with a casing shoe made of steel easily gets cut, due to differences in shapes of mutual threadings in the parts in question. The problems related to preworked threadings in plastic pipes are probably due to the differences of steel and plastic e.g. because of strength and thermal expansion characteristics thereof and the like reasons.
There have been efforts for further development of joint arrangements in plastic pipes with readymade threadings e.g. by using first of all a coupling part coupled with the plastic pipe with a screw joint and on the other hand a very long coupling stem in the casing shoe with necessary elasticity means, such as damping O-rings, despite of which a screw joint between a casing shoe and a plastic pipe to be carried out with reasonable costs has not been managed to reliably accomplish so far. All the types of arrangements described above require unnecessarily massive arrangements in carrying out a screw joint between the casing shoe and the plastic pipe, which is why they increase the manufacturing costs disproportionately and make use of the solutions in question significantly more difficult in practical installation work.
Particularly for the part of a drilling apparatus comprising a rotationally symmetrical pilot and a reamer, there has been found a further need for development of its construction particularly due to the problems related to use of a traditional casing shoe with a view both to metal and plastic pipe drilling, because the type of solutions described above for the mutual coupling of a drilling unit and a casing part by using a casing shoe have been found unsatisfactory.